Electronic circuits contain many (sometimes millions) of components such as resistors, capacitors, inductors, diodes, electro-mechanical switches, and transistors. High density packaging of electronic components is particularly important to allow fast access to large amounts of data in computers. High density electronic circuit packages also are important in high frequency devices and communications devices. The components are connected to form circuits and circuits are connected to form functioning devices. The connections perform power and signal distribution. In a multi-layer electronic circuit package, some layers of the package serve as power planes and other layers serve as signal planes, depending on the operational requirements of the device. The devices require mechanical support and structural protection. The circuits themselves require electrical energy to function. The functioning devices, however, produce heat, or thermal energy which must be dissipated so that the devices do not stop functioning. Moreover, while high density packaging of a number of components can improve performance of the device, the heat produced by the power-consuming components can be such that performance and reliability of the devices is adversely impacted. The adverse impact arises from electrical problems such as increased resistivity and mechanical problems such as thermal stress caused by increased heat.
High density packages necessarily involve increased wiring density and thinner dielectric coatings between layers in a multi-layer electronic circuit package. The layers in a multi-layer package are electrically connected by vias and through-holes. The term "via" is used for a conductive pathway between adjacent layers in a multi-layer electronic circuit package. The term "through-hole" is used for a conductive pathway that extends to a non-adjacent layer. For high density packages the through-holes are increasingly narrow in diameter and the through-holes in each layer must be aligned precisely.
Electronic circuit packages, such as chips, modules, circuit cards, circuit boards, and combinations of these, thus must meet a number of requirements for optimum performance. The package must be structurally sturdy enough to support and protect the components and the wiring. In addition, the package must be capable of dissipating heat and must have a coefficient of thermal expansion that is compatible with that of the components. Finally, to be commercially useful, the package should be inexpensive to produce and easy to manufacture.
Electronic circuit packages, while used in both digital and analog circuits, find their greatest application in digital circuits. In digital circuits a narrow band around one discrete value of voltage corresponds to a logical "0" and another narrow band around a second discrete value of voltage corresponds to a logical "1". Signals having these properties are "digital signals." Digital information processing depends upon the transmission, storage and application of these digital signals.
In digital information processing, a signal changes from one binary level to another. This change is ideally transmitted as a "step function." However, this ideal step function becomes distorted because of resistance, capacitance, inductance, and transmission line effects in the transmission line and in other transmission lines in the package. Moreover, this step function, whether ideal or distorted, gives rise to still other distortions and spurious signals, i.e., noise, and induced signals on other lines in the circuit package. Thus, it is necessary to filter noise out of digital circuits.
Filtering may be accomplished in digital circuit packages by providing internal RC filter circuits of appropriate RC time constant and band pass characteristics, and thereby capacitively coupling, or decoupling, signal lines with, for example, power lines, ground lines, or other signal lines.
Attempts at providing embedded decoupling capacitance are known in the art. For example, in U.S. Pat. No. 5,027,253 to Lauffer, et al, an integral buried capacitor is provided comprising a first electrode connected by a wire to a first signal core and a second electrode connected by a wire to a second signal core. The second electrode at least partially overlaps the first electrode but is separated from it by a thin film of dielectric material. The two electrodes and the thin film of dielectric material define the integral buried capacitor.
In U.S. Pat. No. 5,261,153, to Lucas ("Lucas"), a method is provided for forming a capacitor element internally within a printed circuit board. Lucas discloses arranging uncured dielectric sheets with conductive foils laminated to either side and incorporated as a layer in a printed circuit board.
The method of Lucas requires that clearance holes in the conductive foils be defined by etching through a patterned photoresist material on each foil individually. The present invention allows a multitude of foils to be stacked together and drilled or punched simultaneously, hence creating a lower cost package. Additionally, the Lucas method is subject to reliability problems of plane to plane shorting due to dendritic copper plating along the glass fibers of the thin dielectric material. The non-glass dielectric of the present invention does not contain any defined dendritic copper paths.